Surface acoustic wave devices have been used for filters and duplexers of wireless communication devices such as mobile phone terminals. Recently, acoustic wave devices having a structure designed to have a piezoelectric substance sandwiched between a lower electrode and an upper electrode have attracted attention as the element that has good characteristics at high frequencies and is capable of being reduced in size and made monolithic. Examples of such acoustic wave devices include piezoelectric thin film resonators such as film bulk acoustic resonators (FBARs) and solidly mounted resonators (SMRs).
When large electric power is input to the piezoelectric thin film resonator, harmonics are generated in output signals due to the non-linearity that depends on the polarization direction of the piezoelectric substance. As a method for reducing such harmonics, there has been known a method that divides the piezoelectric thin film resonator as described in, for example, Japanese Patent Application Publication Nos. 2008-85989 and 2007-6495. Additionally, it has been known that a floating capacitance is formed between the electrode of the piezoelectric thin film resonator and the metal layer formed on the underside of the substrate as described in, for example, Patent Application Publication No. 2008-508822. To inhibit the electromagnetic coupling between wiring lines interconnecting the piezoelectric thin film resonators, it has been known to shield the wiring lines as described in, for example, Japanese Patent Application Publication No. 2011-71874.
However, it is newly found that harmonics cannot be reduced even when the piezoelectric thin film resonator is divided.